This section provides background information related to the present disclosure which is not necessarily prior art.
In 1889 when the first electric power transmission line in North America came online, it formed a 4,000 volt connection between the generating station at Willamette Falls in Oregon City, Oreg. and the generating station at Chapman Square in downtown Portland Oreg., some fourteen miles away. In those simple times the notion of a power grid was far from concern. Today, however the situation is quite different. Even ignoring the thousands of small wind powered and solar powered generators, the power grid in North America encompasses approximately 18,000 generators with a combined capacity of over 1.1 TeraWatts. Connecting this network is over 160,000 miles of overhead lines that supply distribution systems that have many more thousands of miles of feeder lines.
To this power grid are attached millions of different loads, ranging from lighting circuits, to heavy induction motors, to telecommunications systems, and to servers that power the Internet cloud. Each of these different loads has unique characteristics. Lighting loads tend to be mostly resistive in nature; inductive loads, such as inductive motors, tend to have a large reactive component in addition to a resistive component. As power engineers will tell you, resistive loads and reactive loads behave quite differently, particularly when system dynamics are considered. When an inductive motor is switched on its coils have a very low inductance, so they act as very low value resistors. This means that you get a surge of current when a motor is first switched on. This can cause a voltage spike on the supply as the supply tries to cope with the high current being drawn. Thus daily usage of the power grid by millions and millions of users inevitably causes surges, brownouts and other dynamic effects that can lead to instability of not carefully monitored.
In addition to usage-based instabilities, the power grid is also exposed to nature, and that introduces another huge source of instability. Lightning strikes, wind and ice storms as well as other natural disasters break power lines, burn out transformers and generators, all which cause power failures. When these failures occur, a portion of the grid being fed by the affected systems may attempt to draw power from other portions of the grid, and this produces other transient surges in the remaining lines as the grid attempts to compensate.
Adding to the effects of daily usage and natural disasters, the power grid is also subject to intentional load shedding, whereby the power utility company will intentionally take certain loads offline, under contractual agreement, to balance loads or to shift loads to a time when demand is lower. By performing load shedding, the power utility company saves cost. This is because the generators used to handle peak demands tend to be powered by more costly fuel sources, such as diesel fuel.
Adding still further to the complexity of the power grid, alternating electric current (AC) is typically generated as three-phase AC current. Doing so allows transmission of the total power with half as much wire. However, it does require three separate phases to be generated and carried by three separate transmission lines. To operate a three-phase system efficiently, the amount of power flowing on each phase should be kept balanced or equal as much as possible. However, because many loads may be connected to only one phase, such as in the typical residence for example, there is no way to guarantee that all phases will be balanced, unless a power engineer monitors the loads and compensates when the loads become too far out of balance.
From the foregoing it should be appreciated that the power grid today is a very complex and dynamic system. Power utility companies today employ computer-implemented software systems that can perform rudimentary monitoring of the health of the power grid. However, due to the complexity of the grid itself, these existing monitoring systems make simplifying assumptions about how to model the power grid. These simplifying assumptions are needed to allow the computer to make predictions about the stability and health of the power grid at a quick enough response rate to be useful to the power engineer.